View SlideshowRequest to buy this photoPhotos by Whitney Cranshaw, Colorado State UniversityIt takes a few years for symptoms of thousand canker disease, including a loss of leaves, to show up in black walnut trees.

For a while, the walnut twig beetle was just another minor pest to the trees for which it was
named.

The same went for a lowly fungus called
Geosmithia morbida.

Then these two nearly anonymous organisms formed an unholy alliance that has become a nightmare
for black walnut trees. That pairing spawned something called
thousand cankers disease.

Thousand cankers was first described in New Mexico in 2001 and since has been found
in nine Western states.

In 2010, walnut trees began to die in Tennessee, Virginia and eastern Pennsylvania.
That’s when Ohio took notice.

Now, Ohio State University Extension researchers are working with state forestry
and agriculture officials on a plan to inspect as many walnut trees as they can find, looking for
signs of the disease.

“We’re going to try to be as proactive in surveying for it as we possibly can,”
said Drew Todd, forest health coordinator for the Ohio Department of Natural Resources. “The sooner
that you can find one of these things, the better.”

Why are they so worried? Ohio already is rife with tree-killers. There are gypsy
moths, Dutch elm disease, emerald ash borers, Asian longhorned beetles and hemlock wooly adelgids,
to name a few.

But back to walnuts.

The walnut twig beetle and
Geosmithia morbida were common pests of the Arizona walnut, a western tree species. The
beetles and their larvae, which tunnel through the soft wood beneath the bark, work as a “natural
pruning agent” by attacking only weakened or diseased limbs.

The fungus wasn’t much of a threat, either. Arizona walnuts quickly seal off
infected areas and minimize damage to their branches.

But at some point, probably in the 1990s, the beetles switched to black walnuts,
and when they did, they carried the fungus with them.

The beetles tunnel into the wood to mate and lay their eggs. They shed spores that
grow and create black cankers around the tunnels.

The cankers spread through the soft wood and the trees’ circulatory systems. As the
fungus cuts off the flow of water and nutrients, leaves wilt and the branches begin to die.

OSU entomologist David Shetlar said adult beetles emerge from infested trees coated
with fungal spores and either move to a new spot on the same tree to dig new tunnels or
spread to nearby healthy walnut trees.

“With that little bite into the plant, they will infect a new tree,” Shetlar
said.

It’s a slow-acting disease. It can take years before people notice the first signs
of it — yellowed wilting leaves, typically in the tops of trees. A mature walnut tree dies within
three years of the first visible symptoms.

So far, there is no treatment for diseased trees. Research efforts are focused on
finding an insecticide or natural parasite to kill the beetles.

“The hope is that there will be some weak link that we can ... introduce,” said Ned
Tisserat, a Colorado State University Extension plant pathologist who was among the first
researchers to identify the disease.

Tisserat said officials in Tennessee, Virginia and Pennsylvania are trying to stop
the disease by cutting down and destroying infected trees. He said the disease is so
widespread in Western states that officials are trying to slow it down by banning the
transportation of infested wood.

No one knows how many trees have been destroyed, but Tisserat said
thousand cankers has wiped out the entire population of walnuts in Colorado Springs.

Black walnuts are not native trees to Western states and largely are used as
ornamental street trees.

The stakes in Ohio are much higher. State forestry officials estimate the value of
Ohio black walnut lumber is $1.2 billion.

In addition, there are 29 farms in Ohio that grow walnut trees, though how much
they produce and their value is not tracked by the state or federal agriculture departments.

Smith said the effort now is to simply determine whether the disease is in Ohio and
to teach people what to look for.

Dan Kenny, an Ohio Department of Agriculture inspection administrator, said he
hopes to conduct a visual survey of walnut trees this summer. The search would focus on forested
campgrounds and other areas where infested wood might have been brought into the
state.

Kenny said the search would begin in August, when leaves of infected walnuts start
to wilt.

Those who suspect infection should send samples to the C. Wayne Ellett Plant and
Pest Diagnostic Clinic at Ohio State, where experts can identify the insect and fungus.

The ideal sample is a branch that’s at least 1 inch thick and 12 inches to 18
inches in length, said Nancy Taylor, the clinic’s director. Branches that have been dead for more
than a month won’t work, Taylor said, because other insects will have infested them.

“Probably, it will be very difficult for a homeowner to sample a tree,” Taylor
said, given that the branches typically start dying at the tops of the trees. “They might need to
work with an arborist.”